Dual automatic radio direction finding system



1945- G. B..GREENE ET AL 2,368,921.

DUAL AUTOMATIC RADIO DIRECTION FINDING? SYS IEM Filed Aug. 1, 1942 2Sheets-Sheet 1 a 11v TER. FREQ.

IN VENT ORSY GEORGE B. GREENE.

PAUL O'CONNOR.

ATTORNEYS.

Feb. 6, G B GREENE ETAL DUAL AUTOMATIC RADIO DIRECTION FINDING SYSTEMFiled Aug. 1, 1942 2 Sheets-Sheet 2 INVENTORS, GEORGE E. GREENE. PAULO'CONNOR.

A TTORNEYS.

Patented Feb. 6, 1945 UNITED STATES? DUAL AUTOMATIC RADIo DIR o'rIoNFINDING SYSTEIVF/"I George B. Greena'Long lfleach anrlv Paul OfCon- 7nor, Los Angeles, Calif., assignorstto .Leo Harvey; La Canada,"Calif.

Application August 1, 1942, Serial No. 453,254

14 Claims.

Our invention relates to dual automatic radio direction finding systems,and more particularly to a 'systemfor-receiving directional indicationsfrom two remote reference radio transmittingexample, the system shown,described and claimed in the Gudie U, S. application, Serial No.399,369, filed June 23, 1941.

In the first application cited above, the two directional elements arerotated to indicate the direction of-the transmitters to which each is]tunedand the relative positions thereof are electrically' applied tocontrol'a rudder servo-motor.

In :the latter application cited above, a radio direction finding systemis utilized in conjunction with each of two reference radio transmittersofkno'wn .location,"the=outputs of the two' se'p-' arat'e'receivingsystems being utilized to operate servo m'otors, oneoperating the rudderof an airplane; the-other mechanically modifying the" operation of' thefirst, in order-that the airplane mi'ghtdfiy a proper course withrespect to the two reference radio stations of known location.

The present application includes tw circuits having directional elementsrespectively controlling servo'motors, but in 'thisinstance provisionhas ibeen madeso that parts of the two circuits are in commonuse withoutinterference between the two-systems. A consequent saving in weight,increase in 'simplicity,and reduction in current demand 'becauseof alesser number of vacuum tllbBSi'lltiliZEd is thereby provided.Furthermore, improved electrical characteristics in the circuitsthemselvesiareinherent. We will, th'ereforeyde' scribewur presentdirection finding-systemasadapted to receive directional signalcomponents from two separatereference radio transmitters of knownlocation, together'with common circuit means; for controllingtwoseparate servo-motors forwhateverpurpose they may he desired to beusedfsuch as,:for example; either of the purposes above'outlined:

Consequently; among tlie'obiects ci cus-interi tion are To :prcvide a'radio dliectifimfiridi system, includingtwodirectionarsignalichannelsgi portions of =which 'areutilizedinccommon why- 52 .duoe weiglittand to reduce pcwewrequirementszr:

to provide a "direction finding systemiwliion does not requirecarriersuppressiontubesz td provide a dual' automatic radio:direotiomlfinderlsystetm utilizing two i directional elements sand asinglefl sense antenna; to provide a dual automaticradiodirection-findingsystem requiringiorrlya ne sense antenna: 1 to pro-videa dual radi'b' directiomfind ing==systemof= relatively simple electricaldesigmc and to provide a'duarradio direction finding sys tem' ofreddcedweight; increased simplicity and having a minimunnpower requirement.-

All ofthe "above objects -comloine to provide' adual automatic=di-r'ecti'crr--'firidin g' *systm -ldeally'a suited'for'use-inairplanes:

our invention possesses-numerousother objects and features of advantage,some-"of-whichi to gether with the'ioregoing; will be"set'"-foi'tl:i"'in the foilowingdescfi'ptiorl ofspecifiii apparatusemb'odying an-d'utilizing our novel:metnod;-" It is therefore to"be'understo'od"that' our methodfls applicable 'to other "apparatus,and".that"-"We' do not limit.ourselvesiinany?wayfitof'tlieiapparatus of'thepresentapplication aswemay adopt. vari ous other apparatus.embodiiiientsfintilizing 'Tth: method, within. the scope of the.appended claimsf In the-drawings.

Figs. 1 and 2 are a schematic" wiring diagram ofone form of circuit-wemayiutilizeembodyin'gf;

. our invention.

Eiipressed in general terms, our inventioncomprisesthe -use i of twodirectional eleinents, vsuch as -rotatab1e loops, for example;.=.eachlfedi'n'g-la loops-preamplifier, .the'se preeamplifi'e'rs .be'inig.modulated byan audio-frequencyoscillator; The..- output. ofrthemodulator-ineaclichannel is ampliw fied in aafirst.radios-frequencyamplifier stagar where .-the-.output-.of the-modulator-is .combinem withthe output ofa sense-antennaa Th esreasult-ant current in each. channel':is then. ampli fied and led to a common intermediateirequencyf.amplifierand-detector;-

Each directional signal radio-frequency chamonel is switched-to operateonlyqon: alternate halfcycles,:' preferablynby the use of a square-wavebias ageneratorasov :thati= modulationi land amplifij cationris takingplaceunmnlyi one channel atmneitime; ltriistheir:possible:toicombinerthe ioutp'ut: of the 'tWCF' directicnalsignalu radio-frequency channels} in -order'iqboz handlethem in a simmerintermediate frequency amplifier and detector unit.

The output of this latter unit may then be passed through a filter,amplified, and the output of the amplifier led to two separate controlor utilization circuits, each containing two trigger tubes controlling aservo-motor. Means are provided to connectthe trigger tube circuits insuch a manner that only the trigger tube circuits corresponding to theparticular directional radio-frequency channel responds to the propersignal, and then only in accordance with the sense of the signal tooperate a servo-motor in the direction as determined by the receiveddirectional signal from one side or the other of the null signalposition of the directional element. Thus, both trigger tube circuitscan operate. 1

We also prefer to utilize a loop gain-controlv circuit so that theoutput of the sense antenna is not criticaL- We may also desire toprovide telephone-channels in order that either one or both ofthe-directional channels can be monitored. The weight of theinstallation is greatly reduced because of the need for only oneintermediate frequency amplifier and detector unit, plate current isconserved because a large number of-the tubes are cut off for one-halfthe operating time, and only one sense antenna need be used.

Our invention may be more fully understood by direct reference to thedrawings. Here, two separate radio-frequency channels A and B areprovided, and as each one is a substantial duplication of the other thedescription will be directed primarily to only one channel whilereference to therother channel will be made now and then where a clearunderstanding of the invention calls for such reference. The duplicatechannel is provided with corresponding primed reference numerals.

Referring, therefore, to channel A, a loop I is provided with a groundedcenter'tap 2, and feeds an input transformer 3. This input transformerleads to thegrid 4 ofv a loop pre-amplifier and modulator tube v5 andalso to an audio-frequency, input transformer 6 fed from a controlsignal frequency oscillator 1, with channels 'A and B fed 1 in push-pullfrom oscillator 1. Input transformer 3 is tuned'by means of variablecondenser l0, and the cathode ll of tube 5 is connected to a. loopgain-control wire |2 through a resistor 14 bi -passed by a condenser l5.The loop gain-control circuit will be later described.

Tube 5 is provided with the usual auxiliary grids I6 'and'l'l. Anode I8of tube 5- is impedance coupled such as through resistor for example,and condenser 2| to a first radio-frequency amplifier tube 22, the anodeof which has a tuned plate circuit 26 connected thereto. The usualauxiliary grid and cathode circuits 2'! are alsoutilized. Input'grid 30-of tube 22, in addition to being coupled to anode I8 of tube'5, is alsoresistance coupled through line 3| to a sense antenna 32, this antennabeing choke loaded by radio-frequency choke 34. Antenna. 32 is coupledto grid 30' in the same manner inchannel B.

The second radio-frequency amplifier-converter stage, comprising tube35, is coupled to tube 22 in the usual manner, with the exception thatthe screen 36 may be provided with a variable voltage from tap 31 inorder to adjust the output of the two channels 'A and B as may seemdenected in the customary manner to have the tube act as an amplifier,by circuits 38. The anode 40 of tube is connected to one half 4| of anintermediate frequency amplifier input transformer 42, the other half 4|of which is energized by anode of channel B. Plate current for anodes 40and 40' is supplied from center tap 44 between two halves 4| and 4| oftransformer 42. Secondary 45 of transformer 42 leads to a singleintermediate frequency amplifier and detector unit 46.

The control grids of tubes 5, 22 and 35 are connected together by biasline 41. Bias is supplied thereto from a square-Wave transformer 45energized by oscillator l, the core of transformer 45 being saturated,so that a square-wave is produced in secondaries 46 and 45. The ends ofsecondaries 46 and 46' lead respectively to bias lines 4'! and 41', thuplacin a square-wave squelching bias on tubes 5, 22 and 35, and 5, 22',and 35', alternately. Thus, only one of the channels A and B is inoperation at any one time, and their outputs will be time displaced, asshown in sketches "50 opposite common transformer 42. Signals fromchannels A and B will therefore pass through, intermediate frequencyamplifier and detector 48 without interference.

The output of intermediate frequency amplifier and detector 48 is thenpassed through-a filter circuit 5| to remove everything but theaudio-frequency therefrom, and led to an output splitting tube 52, suchas, for example, a double triode having one anode 53 feeding twolistening channels LA and LA through amplifying tubes 54 and 54', theoutput feeding listening devices such as receivers 55 and 55. Both grids56 and 5'18 of these listening channel are respectively biased from thesquare-wave busses 41 and 4?, in order that only the output will passtherethrough corresponding to the respective outputs of channels A andB.

Anode 60 of tube 52 feeds tWo control channels CA and CE in parallel.These channels being similar, only channel CA Will be described,'withcorresponding prime numbers applied to channel CB. Channel CA comprisesan audio-amplifier tube '58 hooked up conventionally to feed anaudio-transformer 6| with tuned primary and secondary, resonant atcontrol signal frequency to remove all other audio components, thesecondary 62 of which is provided with a center tap sirable. .Theauxiliary grids in tube 35 are con- 6 64, the outer ends of thesecondary 62 feeding a pair of trigger or thyratron tubes 65 and 55 inpush-pull. The anodes 61 and B8 of the trigger tubes 65 and 56 arerespectively connected together through output coils l8 and l l, theselatter coils being directly coupled to separate phases of a split phasemotor 14 operated from oscillator In this case oscillator l is shownseparately indicated to avoid long connection lines on the drawings, theconnection in channels CA and CB being of opposite phase from thisoscillator. Cathodes l5 and 16 respectively of trigger tubes 65 and 66are connected together,'and to a battery resistor ll .through whichbattery current flows so that a D.-C. cathode biasing means is provided.The action of this bias will be referred to later in describing theoperation of the trigger tubes.

Loop gaincontrol circuits GA and GB are also fed from anode of tube 52to provide a rectified control signal frequency component of the audiooutput, after filtering and voltage amplification. These circuits arealso identical, and only circuit GA will be described, GB carryingcorresponding assassinaprimed numerals. Circuit. GA comprises: anifamplifier. tube .80 feeding 'asfull wave rectiflerrtl; the output of whichpasses through .a smoothing or filter circuit 82, this output then beingapplied through loop gain-control line l2 to cathodell of theloop-preamplifier. modulator tube15 in:

channel A. The output of circuit GB is, of course, applied to channel B.

It is also advisable to utilize an automatic vol ume'control on each ofchannels A and-B. Consequently, automatic volume controls 85 and'BS ofconventional design,rare fed from cathode load resistor of a diodedetector. tube, theoutput. of: automatic volume control 85 and 85 being.fedthrough lines 86 and 86' to the other side ofseccndaries 46 and 45 ofsquare-wave transformer 45, so'that thesquare-wave bias issuperimposedon the automatic volume control-bias In describing theoperation of the dualautomaticradio direction finder system just abovedescribed, it may be assumed that thesystem is.

installed in an airplane and it is desired, for

example, that the loops I and l are'to-be con trolled as to rotation bymotors i4 and M so that the loops i and i will respectively indicate bynull reception the. position of two different reference radiotransmitters of known location. Channel A is therefore tuned to oneofthese radio transmitters and channel B is tuned to the other. It willtherefore be seen that if loops-I or i should become, due to variationin course of the airplane, orientated so that the null axis ofthe loopwas at one side or the other of a straight line joining the loop withthe reference station, that a radio-frequency signal will be received bythe loop, the sense of this signal as to phase bein 'in accordance withwhether the loop null axis was at one side or the other of the directionline joining the loop with the distant station.

The signal from'loop i is fed into the loop preamplifier and modulatortube 5. Similarly a signal is fed'from loop I into the correspondingtube 5'. Disregarding for the moment any A. V. C. component in theoutput circuit of the squarewave transformer 35, the square-wave signalwill render channels A and B only alternately operative. Oscillator lexerts a bias upon the tube 5 which is synchronous with the square-wavepulse and which is of control signal frequency, so that during theperiod through which the square-wave bias has rendered tube 5 operative,the voltage from oscillator i will modulate the output of tube 5. Noattempt need be made to provide a balanced modulator since we areconcerned with a demodulator control signal frequency voltage onlyduring this period through which tube 5 is operative. Further, we :willdispense with the customary suppression of carrier in our modulatorstage since the carrier component of the loop output will always appearatmixing in the input circuit of tube 22 to be 90 degrees out of phasewith the sense-antenna output and so therefore, will add in quadratureand cannot possibly distort the between theachannelsiA randExheuausemnlymne; channel. is .operating at? any one time: 1

The voutput offtubes 2 2: and i. 2 therefor "con sistiof. aradio-frequency..-.pulse witnilocallwsupi-i. plied side-bands of controlsignal frequency-the sense of which sideebands :corresponds: to" I therelative sense I of radio-frequency signal received by. loop .I lwithlrespect. toithe radio fre quency. signal received. by the:sen'see-antennaa: Thus the L pulse whose durationis one"'half':cycle:Of".COI1'- trolled'signal' frequency, may demodulatezas either apositive swing. orra negativeswing; depending upon the aforedescribed.relative sense.

Thesesignals areitheniamplified and: converted to intermediatefrequency; by tubes-35 and. .35, mixed in transformer 42 and passed.through the intermediate. frequency amplifier "and adetector, r thenpassed-through filter -5l intooutputtubetz i as audio'positive ornegative pulses. From output tube 52, considering now only thecontrolcircuits CA and CB, the audio currents :are passed. to' the triggertubes Withilihfiir grids positioned in" pushpull relationship, their.anodes" being supplied by oscillator =1 in-parallel,:the.anodes being ofopposite phase infeac'h'of channels CAandCB.

When the trigger tuberianode potentials are in parallel; asshown incontrol circuits CAand CB. it is only the half cycle corresponding: tothe :positivegswingof the anode potentials that is of any use intriggering aetube. Consequently, the demodulated control signalzi usefulonly on the half cycle corresponding to positive anode potentials.Because of this fact itis not necessary to apply the square-wavebiastocontrol :circuits: CA and CB if the controlsignal oscillator! i'.connected to control circuits CA and'CB out. of phase, cor respondingto the phases. in which loop pre amplifier and modulator'tubes 5 and 5'are modulatedin push-pull in radio-frequency channels A. and B..Thus,.even though the mixed signals. are presented to all four triggertubes, only one or the other of the triggertubes-in the same channelwill fire at the proper time, because. of the -.fact,. forexample,thatwhen-theanodes of the trigger" tubes in channel .CA are positive andare able to fire, the anodes-of the trigger tubes in channel CB arenegative and the tubesaare'not' abl to fire.

signals from radio-frequency .channel .A- cannot 'fire thetrigger-tubesin control channel:; CB, but can fire one or "the-other ofthe trigger tubes in channel CA. vThesame applies to channel Bandcontrolchannel-CB..-

This control circuit, where the grids of the trigger tubes are connectedin push-pull. but where the'anodes are connectedin parallel, is alsohighly desirable when used in conjunctionewith the cathode biasingcircuit 11. It will clearly be seenfrom this .circuit that the firedtube will draw grid current. This current, flowing through. thecathodezbiasing resistance, will cause an increase incathode potentialproportional to current and resistance joint1y.- The increasedcathode'poten-. tial thus obtained will, of cours'e b impressed as: abias upon both cathodes alike,:but, since the first tube fired willremain fired for the duration of thehalf cyclewithout regardto alteredgridcathode potential,v the reduced sensitivity caused by this biasafiects only theunfired tu be, andrwill cause it to remain unfired forthe duration of the firing half-cycle. The aboveoperationwill be re--peated. on each subsequent positive half-cycleior example,-and willcause only one tube tobe fired at anyone instant without regard toanyr-unwanted :noise. components appearing upon athe trigger; tube:gridsls A sensitivity:reduction .for

example, of from six to eight volts for the duration of the half-cyclcan be obtained on the idle tube by the firing of the other tube. Thus,the undesired firing of the idle tubeis substantially eliminated.

The loop gain-control circuit utilized herein is substantially the sameas the loop gain-control circuit disclosed in the prior Greene U. S.application, Serial No. 438,488,'filed April 10, 1942, and applies arectified component of the control signal frequency output to the looppre-amplifier and modulator tube, so that the loop gain can be mademaximum adjacent the .null position of the loop without danger ofexceeding the sense antenna input at other positions of the loop.

The A. V, C. controls which are applied to the radio-frequency tubesthrough the square-wave busses 4'1 and 41 from the respective channels Aand B, are set to provide maximum sensitivity in all of theradio-frequency tubes at zero A. V. C. level. The A. V. C. current ispassed through the square-wave generator transformer 45 and consequentlythe square-wave potential floats up and down, with maximum sensitivityat the point where the tubes are just cut off by the negative portion ofthe'square-wave cycle. The A. V. C. level is then reduced for minimumsensitivity, or a maximum A. V. C. bias, so that the cut-off portion ofthe square-wave cycle never rises above cut-off but always drops belowcut-off. Thus, the tubes in channels'A and B can never be active at thesame time even with A. V. C. control.

Thus it will be seen that while the loop gaincontrols from circuits GAand GB act only on tubes 5 and 5' to regulate the loop gain with respectto the sense antenna signal, the A. V. C. control operates to controlthe signal level through the entire radio-frequency amplifier sectionprior to the injection of the signal into the single intermediatefrequency amplifier and detector.

A number of advantages are inherent in the type of system shown,described and claimed herein. In the first place the entire intermediatefrequency amplifier and detector is in common use and consequently neednot be duplicated. A saving in weight and power consumption is thusobtained. Due to the fact that each channel operates only on'one-half ofthe modulating cycle, the necessity for using customarily employedcarrier suppressor circuits is avoided, thus further eliminatingequipment and power consumption. The tubes in the two channels takeplate current onl during one-half of the cycle of the control frequencyoscillator, thus both channels together consume no more anode power thana single channel. One sense antenna can be eliminated, and the singlesense antenna remaining can be coupled into the circuit resistively,thereby removing the disadvantages of antenna mixing coils. Asignificant overall saving in weight and overall power-consumption istherefore provided without loss of accuracy, sensitivity, or control.

We claim:

1. A direction finder system comprising a pair of directional receivingcircuits, one being tunable to the carrier frequency of one station, theother being tunable to the carrier frequency of another station, a pairof utilization circuits, common amplifier and detector means couplingsaid utilization circuits to said directional receiving circuits, andmeans for causing both said directional receiving circuits andsaidutilization circuits to be alternately operative-at a similarperiodicity whereby each of said utilization circuits will be responsivein accordance with the output of only one of said directional receivingcircuits.

2. A direction finder system comprising a pair of directional receivingcircuits, one being tunable to the carrier frequency of one station, theother being tunable to the carrierfrequency of another station, a senseantenna circuit coupled to both of said directional receiving circuitsin common therewith, a pair of utilization circuits, common amplifierand detector means coupling said utilization circuits to saiddirectional receiving circuits, and means for causing both saiddirectional receiving circuits and said utilization circuits to bealternately operative at a similar periodicity whereb each of saidutilization circuits will be responsive in accordance with the output ofonly one of said directional receiving circuits.

3. A direction finder system comprising a pair of directional receivingcircuits, one being tunable to the carrier frequency of one station, theother being tunable to the carrier frequency of another station, meansfor impressing a signal on the carrier in each of said directionalreceiving circuits, a sense antenna circuit coupled to both of saiddirectional receiving circuits in common therewith, a pair ofutilization circuits, common amplifier and detector means coupling saidutilization circuits to said directional receiving circuits, and meansfor causing both said directional receiving circuits and saidutilization circuits to be alternately operative at a similarperiodicity whereby each of said utilization circuits will be responsivein accordance with the output of only one of said directional receivingcircuits.

4. A direction finder system comprising a pair of directional receivingcircuits, one being tunable to the carrier frequency of one station, theother being tunable to the carrier frequency of another station, a senseantenna circuit coupled to both of said directional receiving circuitsin common therewith, and means for alternately combining the output ofsaid sense antenna circuit with that of each of said directionalreceiving circuits.

5. A direction finder system comprising a pair of directional receivingcircuits, one being tunable to the carrier frequency of one station, theother being tunable to the carrier frequency of another station, meansfor alternately suppressing the output of each of said'directionalreceiving circuits to produce an interrupted output of one directionalreceiving circuit which is time displaced from the correspondinglyinterrupted output of the other directional receiving circuit, commonmeans for amplifying said time displaced outputs, and means forsubsequently utilizing such amplified outputs in the guiding of avehicle along a predetermined course;

6. A direction finder system comprising a pair of directional receivingcircuits, one being tunable to-the carrier frequency of one station, theother being tunable to the carrier frequency of another station, meansfor alternately suppressing the output of each of said directionalreceiving circuits to produce an interrupted output of one directionalreceiving circuit which is time displaced from the correspondinglyinterrupted output of the other directional receiving circuit, commonmeans for amplifying and detecting said time displaced outputs, a pairof branch utilization circuits coupled to said common amplifying anddetecting means, and means for alternately rendering said branchcircuits responsive to the output of said common amplifying anddetecting means-atthe same-rate as the'alternate' =suppres-' sion of Isaid directional receiving circuits,- whereby 'each of-saidbranchutilization circuits is caused to respondinaccordance withthe output ofone of said directionalreceiving'circuits.

7. A direction finder system comprisingapair of directionalreceiving-circuits, one being tunable to'the carrier frequencyofone'station, the other being tunable to the-carrier frequency 'ofanother station, a sense antenna circuit coupled'to both of saiddirectional receivingcircuits and-in'com-' mon therewith, means foralternately combining the-output ofsaid 'sense antenna circuit with thatof each of said directional receivingcircuit's to produce periodicallycombined outputs which are time displaced from each other, commonmeansfor amplifying said time displaced outputs, and means for subsequentlyutilizing such amplified outputs in the guiding of a vehicle along apredetermined course.

8. A direction finder system comprising a pair of directionalreceiving-circuits, one being tunable to the carrier frequency of onestation, the other being tunable to the carrier frequency of anotherstation, means for modulating the received carrier in each of saiddirectional receiving circuits, a sense antenna circuit coupled to bothof said directional receiving circuits and in common therewith, meansfor alternately combining the output of said sense antenna circuit withthat of each of said directional receiving circuits to produceperiodically combined outputs which are time displaced from each other,common means for amplifying said time displaced outputs, and means forsubsequently utilizing such amplified outputs in the guiding of avehicle along a predetermined course.

9. A direction finder system comprising a pair of directional receivingcircuits, one being tunable to the carrier frequency of one station, theother being tunable to the carrier frequency of another station, a senseantenna circuit coupled to both of said directional receiving circuitsand in common therewith, means for signal modulating the receivedcarrier of each of said directional receiving circuits, means foralternately combining the output of said sense antenna circuit with thatof each of said directional receiving circuits to produce combinedoutputs which are time displaced from each other, common means foramplifying and detecting signal variations in said time displacedoutputs, and means for separating the detected signals originating inone receiving circuit from those originating in the other and utilizingsuch amplified signal variations in the guiding of a vehicle along apredetermined course.

10. A direction finding system comprising a pair of directionalreceiving circuits, one being tunable to the carrier frequency oftransmission of one station, the other being tunable to the carrierfrequency of another station, amplifyin means common to said pair ofdirectional receiving circuits and adapted to amplify the output fromeach of said directional receiving circuits, a pair of utilizationcircuits coupled to said common amplifying means and adapted to functionin accordance with signal variations in the output of said directionalreceiving circuits, means for periodically and alternately suppressingthe signal output from said directional receiving circuits to saidcommon amplifier means, and means for periodically and alternatelyrendering said utilization circuits responsive to signal energy fromsaid common amplifier means the receiving circuit outputtosaidcommonamplifying means whereby each utilization circuit can be madeto respond exclusively to the signal variations of but one ofsaid pairof directional receiving circuits.

11. A direction finding system comprising a pair of directionalreceiving circuits, one'being tunable to the carrier frequencyof onestation, the other being tunable to the'carrier frequency of anotherstation, a sense antenna circuit coupled to and in common with saiddirectional receiving circuits, amplifying means common to said 'pair ofdirectional receivingcircuits and adapted to amplify the output fromeach of said directional receiving circuits,-a pair 'of utilizationcircuits coupled'to'saidcommon amplifying ,m'eans and adapted "tofunction in-accordance with signal variations 'in'-the'=-output of saiddi'"-' rectional receiving circuits, means for periodical- I ly andalternately suppressing the signal output from said directionalreceiving circuits to said common amplifier means, and means forperiodically and alternately rendering said utilization circuitsresponsive to signal energy from said common amplifier means and at thesaid periodicity as the suppression of the receiving circuit output tosaid common amplifying means, whereby each utilization circuit can bemade to respond exclusively to the signal variations of but one of saidpair of directional receiving circuits.

12. A direction finding system comprising a pair of directionalreceiving circuits, one being tunable to the carrier frequency of onestation, the other being tunable to the carrier frequency of anotherstation, means for modulating the received carrier in said directionalreceiving circuits, a sense antenna circuit coupled to and in commonwith said directional receiving circuits, amplifying and detector meanscommon to said pair of directional receiving circuits and adapted toamplify the output from each of said directional receiving circuits, apair of utilization circuits coupled to said common amplifying means andadapted to function in accordance with si nal variations in the outputof said directional receiving circuits, means common to said directionalreceiving circuits and said utilization circuits for periodically andalternately rendering corresponding receiving and utilization circuitsinoperative whereby each utilization circuit can be made to respondexclusively to the signal variations of but one of said pair ofdirectional receiving circuits.

13. A direction finding system comprising a pair of directionalreceiving circuits, one being tunable to the carrier frequency of onestation, the other being tunable to the carrier frequency of anotherstation, a sense antenna circuit coupled to and in common with saiddirectional receiving circuits, amplifying and detector means common tosaid pair of directional receiving circuits and adapted to amplify anddetect the output from each of said directional receiving cir cuits, apair of utilization circuits coupled to said common amplifying anddetector means and adapted to function in accordance with signalvariations in the output of said directional receiving circuits, meansfor periodically and alternately suppressing the signal output from saiddirectional receiving circuits to said common amplifying and detectormeans, and means for alternately rendering said utilization circuits responsive to signal energy from said common amplifying and detector meansand at the same andat the same periodicity as the suppression of theother being tunable to the carrier frequency 10 of another station,means for modulating the received carrier in said directional receivingcircuits, a sense antenna circuit coupled to and in common with saiddirectional receiving circuits,

amplifying and detector means common to said 15 pair of directionalreceiving circuits and adapted to amplify and detect the output fromeach of said directional receiving circuits, a pair of utilizationcircuits coupled to said common amplifying and detector meansand-adapted to function in accordance with signal variation in theoutput of said directional receiving circuits, a square wave oscillatorconnected in push-pull to said pair of directional receiving circuitsfor periodically and alternately suppressing the signal modulated outputfrom said directional receiving circuits to said common amplifying anddetector means, and means for periodically and altemate- 1y renderingsaid utilization circuits responsive to signal energy from said commonamplifying and detector means at the frequency of said square waveoscillator whereby each utilization circuit can be made to respondexclusively to the signal variations of but one of said pair ofdirectional receiving circuits.

GEORGE B. GREENE. PAUL OCONNOR.

